Circulatory System Notes (Bio 11 Unit 3)

Overview of the Circulatory System

• The circulatory system is a transport network responsible for moving blood, gases, nutrients, hormones, and waste products throughout the body.
• Functions:
  • Delivering oxygen to body tissues.
  • Removing carbon dioxide and other waste.
  • Distributing nutrients from digestion.
  • Transporting hormones from glands.
  • Defending against pathogens (via white blood cells).
  • Maintaining body temperature and homeostasis.

Structure of the Circulatory System

• Three main components:
  1. Heart: the pump.
  2. Blood vessels: tubes that carry blood.
     • Arteries: carry blood away from the heart (typically oxygenated).
     • Veins: carry blood toward the heart (typically deoxygenated).
     • Capillaries: tiny vessels where gas and nutrient exchange occurs.
  3. Blood: the fluid that transports substances.
     • Plasma: liquid portion, mostly water.
     • Red blood cells (erythrocytes): carry oxygen using hemoglobin.
     • White blood cells (leukocytes): immune function.
     • Platelets: clotting.

Structure of the Heart

• The heart is a muscular, four-chambered organ, about the size of your fist.
• Located slightly left of center in your chest and protected by the rib cage.
• Divisions:
  • Right atrium
  • Right ventricle
  • Left atrium
  • Left ventricle
• Each side has an atrium (upper chamber) and a ventricle (lower chamber).
• Major vessels of the heart:
  • Vena cava (superior & inferior): brings deoxygenated blood to the right atrium.
  • Pulmonary artery: carries blood from the heart to the lungs.
  • Pulmonary veins: carry blood from the lungs to the heart.
  • Aorta: largest artery, carries oxygenated blood to the body.
• Heart valves (prevent backflow):
  • Tricuspid valve (right AV valve)
  • Pulmonary valve (semilunar)
  • Mitral/bicuspid valve (left AV valve)
  • Aortic valve (semilunar)

Blood Flow Through the Heart – "Figure 8" Pathway

• Blood makes two loops:
  1. Pulmonary circulation (to the lungs and back).
  2. Systemic circulation (to the body and back).
• Step-by-step blood flow:
  1. Deoxygenated blood from the body enters the right atrium via:
     • Superior vena cava (from head and arms)
     • Inferior vena cava (from lower body)
  2. Blood passes through the tricuspid valve into the right ventricle.
  3. The right ventricle pumps blood through the pulmonary valve into the pulmonary artery, which goes to the lungs.
  4. In the lungs, blood picks up oxygen and releases CO₂.
  5. Oxygenated blood returns to the heart via the pulmonary veins and enters the left atrium.
  6. Blood passes through the mitral (bicuspid) valve into the left ventricle.
  7. The left ventricle pumps blood through the aortic valve into the aorta.
  8. The aorta distributes oxygenated blood to the entire body through systemic circulation.
• The "figure 8": one loop to the lungs, one to the body.

Unique Features of the Heart

• Thicker left ventricle: needed to pump blood to the entire body (more pressure).
• Septum: separates oxygenated and deoxygenated blood (prevents mixing).
• Valves: ensure one-way blood flow.
• Pacemaker (SA node): group of cells in the right atrium that control heartbeat.
• Coronary arteries: supply the heart muscle with oxygen.

Types of Blood Vessels

1. Arteries
   • Carry blood away from the heart.
   • Thick muscular walls.
   • High pressure.
   • No valves.
   • Largest = aorta.
2. Veins
   • Carry blood toward the heart.
   • Thinner walls.
   • Lower pressure.
   • Have valves to prevent backflow.
   • Largest = vena cava.
3. Capillaries
   • Microscopic.
   • Very thin walls (1 cell thick).
   • Site of gas exchange.
   • Connect arterioles and venules.

Pulmonary vs. Systemic Circulation

Connection to Respiratory System

• The circulatory and respiratory systems work together to deliver oxygen and remove CO₂.
• Connection:
  • Lungs (part of the respiratory system) oxygenate blood.
  • Pulmonary capillaries surround alveoli (air sacs).
  • Gas exchange occurs by diffusion:
    • Oxygen moves into the blood.
    • Carbon dioxide moves out into the lungs.
• Oxygen is transported in the blood by red blood cells, bound to hemoglobin.

Key Terms & Concepts

Visual Summary: The "Figure 8" Flow

• Right side of the heart is low in oxygen and pumps blood to the lungs to get oxygen.
• Left side of the heart is high in oxygen and pumps blood to the body.
• Flow: Body → Vena Cava → Right Atrium → Right Ventricle → Pulmonary Artery → Lungs → Pulmonary Vein → Left Atrium → Left Ventricle → Aorta → Body

Nova Scotia Biology 11 Curriculum

• Understand how blood circulates through the body and lungs.
• Identify all heart chambers and valves.
• Distinguish between pulmonary/systemic circulation.
• Describe how blood pressure and flow are regulated.
• Link respiration and circulation for oxygen delivery and carbon dioxide removal.